National Grid (Western Power, as I still refer to them) are very good, it worth getting back intouch with them to fit an 80A fuse. Hopefully you will get a different contractor or gang If the three cables are the same size, it could be two neighbours are looped from the main supply in your house. Whils’t its not common, its also not unheard of.
This picture is from before we had the Ev charger installed and had a new smart meter installed, as these ones never ever connected or sent data. One I sent to Ohme for the EV install survey.
The smaller box to the far left and the wire going up is next door’s supply, and it comes back into the top of our cut-off.
EX30 SMER Ultra